As a conventional art, Patent Literature 1 discloses an example of the aforementioned vehicle body side structure for a vehicle. As illustrated in FIG. 9, the vehicle body side structure disclosed in Patent Literature 1 is provided with a center pillar 83 including a center pillar outer member 81 and a center pillar inner member 82, and extending in the vehicle up-down direction; a pair of left and right roof side rail portions 84 (in FIG. 9, only one of the roof side rail portions 84 is illustrated) disposed on the upper side of the center pillar 83, and extending in the vehicle front-rear direction; and a roof reinforcement 86 extending in the vehicle width direction along the lower surface of a roof panel 85, and configured to connect between the left and right roof side rail portions 84 at the position corresponding to the center pillar 83.
Each of the roof side rail portions 84 includes a roof side rail outer member 87, a roof side rail inner member 88, and a roof side reinforcement 89. The roof panel 85 includes a flange portion 85a at a one-step lower position on the outer side thereof in the vehicle width direction. The roof side rail outer member 87 includes a flange portion 87a at a one-step lower position on the inner side thereof in the vehicle width direction. The roof side rail inner member 88 includes a flange portion 88a at the upper end thereof. The flange portion 87a of the roof side rail outer member 87, the flange portion 88a of the roof side rail inner member 88, and the flange portion 85a of the roof panel 85 are fixed to each other by welding.
The roof reinforcement 86 includes an upper surface portion 86a which comes into contact with the roof panel 85, a bottom surface portion 86b, and a vertical wall portion 86c for vertically connecting between the upper surface portion 86a and the bottom surface portion 86b. The roof reinforcement 86 has an upside-down hat shape in side view.
The upper surface portion 86a of the roof reinforcement 86 includes an outer end and its vicinity in the vehicle width direction, which are configured such that the height is gradually decreased toward the outer end of the roof reinforcement 86. A joint piece 90 is integrally formed at the outer end of the upper surface portion 86a. The joint piece 90 is welded to each of the flange portions 85a, 87a, and 88a. 
Specifically, the height position of the flange portion 85a, 87a, 88a is lower than the height position of the joint piece 90. Therefore, the height of the upper surface portion 86a of the roof reinforcement 86 is gradually decreased toward the outer end of the roof reinforcement 86 so that the height position of the joint piece 90 is equal to the height position of the flange portion 87a. 
Further, a gusset 91 as a strength reinforcement member is provided between the bottom surface portion 86b of the roof reinforcement 86, and the roof side rail inner member 88 of the roof side rail portion 84 for connecting between the bottom surface portion 86b and the roof side rail inner member 88.
In the conventional structure illustrated in FIG. 9, however, the height position of the joint piece 90 is limited by the height positions of the flange portions 85a, 87a, and 88a. 
Further, at the time of side collision of a vehicle, a side collision load is input to the center pillar 83. Then, a moment of rotation illustrated by the arrow C in FIG. 9 is applied to the roof side rail portion 84 as a reaction of the side collision load. As a result, the roof side rail portion 84 intrudes inwardly in the vehicle width direction accompanied by pivotal movement of the roof side rail portion 84 by the moment of rotation. When the aforementioned phenomenon occurs, the roof reinforcement 86 fails to completely receive the side collision load, because the cross sectional space around the end of the roof reinforcement 86 is small due to the aforementioned structure, in which the height of the upper surface portion 86a is gradually decreased at the end of the roof reinforcement 86. Consequently, it may be impossible to transfer the side collision load to the roof side rail portion on the opposite side in the vehicle width direction.